How To Correctly Build libdatachannel For Android

[TryRevilo]

Hi Ageneau. I've been trying to set build your library libdatachannel for an Android project. I've tried both build options you gave :

• POSIX-compliant operating systems, and
• Build directly with Make.

I, however, keep getting the following error when I try to build the project in Android Studio C/C++ :

ld: error: ../../../../libs/libdatachannel/libdatachannel.a(wstransport.o) is incompatible with aarch64linux.

Would you please advise on how to get it working? How can I build it so that I get ARM builds for Android? Any way you can help will be greatly appreciated.

Thank you in advance.

---

P.S : Thanks for such a great library.

[paullouisageneau]

Hi, it looks like libdatachannel is not built for the required ARM64 architecture. The easiest way to build it for the right target is to use the Android NDK toolchain file, something like:

$ cmake -B build -DUSE_GNUTLS=0 -DUSE_NICE=0 -DCMAKE_BUILD_TYPE=Release -DCMAKE_TOOLCHAIN_FILE=[Path to the NDK]/build/cmake/android.toolchain.cmake -DANDROID_ABI=arm64-v8a -DANDROID_PLATFORM=[min SDK version]

[TryRevilo]

Hi thanks for the reply Ageneau.

I tried that :

cmake -B build \
    -DUSE_GNUTLS=0 -DUSE_NICE=0 \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_TOOLCHAIN_FILE=/home/rev/Downloads/rev_data/rev_progs/rev_android_studio/rev_ndk/android-ndk-r25b-linux/android-ndk-r25b/build/cmake/android.toolchain.cmake \
    -DANDROID_ABI=arm64-v8a -DANDROID_PLATFORM=21

It builds fine without errors. However, when I :

$ cd build  
$ make -j2  

it all goes well untill :

3 warnings generated.
[ 70%] Building CXX object CMakeFiles/datachannel.dir/src/impl/transport.cpp.o
[ 70%] Building CXX object CMakeFiles/datachannel.dir/src/impl/verifiedtlstransport.cpp.o
[ 70%] Building CXX object CMakeFiles/datachannel.dir/src/impl/websocket.cpp.o
[ 72%] Building CXX object CMakeFiles/datachannel.dir/src/impl/websocketserver.cpp.o
[ 72%] Building CXX object CMakeFiles/datachannel.dir/src/impl/wstransport.cpp.o
[ 74%] Building CXX object CMakeFiles/datachannel.dir/src/impl/wshandshake.cpp.o
[ 74%] Linking CXX shared library libdatachannel.so
ld: error: /home/rev/Downloads/my_open_ssl/libs/libssl.a(libssl-lib-d1_srtp.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libssl.a(libssl-lib-methods.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libssl.a(libssl-lib-ssl_cert.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libssl.a(libssl-lib-ssl_init.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libssl.a(libssl-lib-ssl_lib.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libssl.a(libssl-lib-ssl_rsa.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libssl.a(libssl-lib-ssl_sess.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libssl.a(libssl-lib-ssl_stat.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libssl.a(libssl-lib-statem.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-a_int.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-bio_lib.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-bio_meth.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-bss_mem.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-bn_lib.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-bn_rand.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-ec_key.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-err.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-e_aes.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-evp_enc.o) is incompatible with aarch64linux
ld: error: /home/rev/Downloads/my_open_ssl/libs/libcrypto.a(libcrypto-lib-evp_lib.o) is incompatible with aarch64linux
ld: error: too many errors emitted, stopping now (use -error-limit=0 to see all errors)
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
CMakeFiles/datachannel.dir/build.make:934: recipe for target 'libdatachannel.so' failed
make[2]: *** [libdatachannel.so] Error 1
CMakeFiles/Makefile2:352: recipe for target 'CMakeFiles/datachannel.dir/all' failed
make[1]: *** [CMakeFiles/datachannel.dir/all] Error 2
Makefile:135: recipe for target 'all' failed
make: *** [all] Error 2

I think it is something with my OpenSSL setup.

I have tried various OpenSSL Build and Install approaches including :

• sudo apt-get install libssl-dev

• From Git Source Repo

$ git clone git://git.openssl.org/openssl.git
$ ./Configure
$ make
$ make test

My System :

$ lsb_release -a

No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.6 LTS
Release: 18.04
Codename: bion

Could you please advise on what I might be still doing wrong or missing?

Thank you in advance.

[paullouisageneau]

You need to cross-compile OpenSSL for Android and for the right ARM architecture, you can't use a build targeting your computer.